Optimized Design of a Dynamically-Based Motion Generating Spatial Four-Bar Mechanism on Rigid Multibody Systems
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Date
2009-10
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Addis Ababa University
Abstract
The four-bar spatial mechanism is the most basic chain that can be composed of four links and
can include joints with any combination of rotational and translational freedom used in
thousands of applications. This thesis will present some of the techniques and introduce solution
tools that were not needed for planar motion. One of the new techniques known as the Euler
parameters will be considered in this work.
The thesis includes modeling, optimizing computer-aided dynamic analysis and simulation
of four-bar spatial mechanism composed of rigid bodies that are used for different applications of
spatially moving motion generating mechanisms. The Motions of the rigid bodies are predicted
by numerically integrating Differential-Algebraic Equations (DAEs) developed from principles
of mechanics by the Newton-Euler’s approach.
The computer program, MSC.ADAMS2005 will be used to model, solve, simulate, and optimize
the dynamics of the appraised spatial four-bar mechanism as a lens-polishing mechanism by
integrating the differential equations.
Unlike analytical synthesis, optimization allows direct incorporation of a greater number of
design constraints, thus resulting in solutions that are more practical. In this thesis, an efficient
algorithm known as the Generalized Reduced Gradient (GRG) is used to synthesize all kinematic
linkages of the spatial mechanism. This approach will allow monitoring and controlling
objectives and constraints, which will yield practical solutions to realistic mechanism design
problems with lower kinematic pairs.
In addition to the above mentioned points, a mobility analysis has been done for the RSSR
mechanism, which is a one degree of freedom, single loop, and spatial mechanism.
Thus, this thesis specifically discusses a practical example of a lens polishing four-bar spatial
mechanism that simply substitutes the extremely expensive existing polishing robots. This
mechanism is applicable in polishing lenses of military fire control instruments found in the
Ethiopian Defence Forces. Thus, the design presented in this thesis provides a relatively low-cost
solution for the existing problem as compared to the robots. This can be created with ease of
manufacture in a machine shop quickly and simply. Numerical results obtained in this thesis are
compared with existing literatures.
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Keywords
Spatial Four-Bar Mechanism, Dynamically-Based Motion, Optimized Design, Rigid Multibody Systems